Method of making a bumper bar



Sept. 19, 1939. E. M. BAKER 2,173,092

METHOD-0F MAKING A BUMPER BAR Filed July 1:2,v 1957 Hof/QOLL//VG 1500- '1900 "E Caf/www@ @say f2/vb 54 95T P19566' Opf/P19770 A @W Q05 Patented sept.' 19, 1939 UNITE-p' sTAras PATENT oF-Ficr.

METHOD or MAKING .1i` Bumm: Ban

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Application July 12, 1937, serial No. 153,19c 4 claim. (ci. 29-152) This invention relates to a. method of making a bumper bar or like article, and more particularly to an vimproved method of, making ferrous metal articles that are to be bright plated.

.In the manufacture of bumper bars and like articles, where the articles are to receive bright or mirror-like coatings of nickel, or nickel and chromium plate, the builng and polishing operal tions'required represent a considerable propor- 'w tion of the total cost of manufacture. Unless the surface of the article to which the nickel,

or nickel and chromium plate are to be applied,

is highly polished, the finished plated article will not present a bright, mirror-like surface.

In' accordance with the present invention, an age hardenablesteel, such as a copper alloy steel, is used as a starting material in the manufacture of bumper and like articles. An ingot or billet of such age hardenable steel is rst subject 20 toa hotnrolling operation to reduce the ingot or billet to the form of a semi-nished sheet of somewhat greater thickness than that of the nished article. The hot rolled, semi-huished sheet is next cooled under such conditions as to prevent precipitation of the age hardening constituents of the alloy steel. After subjecting the semi-nlshed sheet to a pickllng or other cleaning operation, it is next cold rolled to the desired A thickness and to produce a high surface nish. 30 Thereafter, the senil-finished sheet is suhiected to the usual processes, such as trimming, punching, forming to shape, and the like, now employed in the manufacture of bumpers, and after being washed to remove oiland lubricating com- 31 pounds, the formed bumpers are subjected to heat treatment in an atmosphere controlled furnace to age harden the steel alloy without destroying the ne surface nish. .Preferablyy a reducing or `mori-oxidizing, and non-decarburlzing atmosphere is employed in the he'at treatment furnace and the bumpers yare delivered from the furnacel in a cold condition, so that they are then ready to ybe plated with little or n'o buihngor polishing required. Y 45 It is therefore an important object of this invention to provide an improved method for the manufacture of bumper bars and like articles that are to receive a bright metal plating, such as nickel, or nickelI and chromium plating, whereby the bulng or polishing of the metal article prior to the platingzthereof, or between successive platings, is largely eliminated andthe cost 'of manufacture correspondingly reduced.

It is a further important object of this in- 55 vention to provide a method of preparing bumper less than 1%.

b'ars and like articles' from an age hardenable alloy steel by a succession of operations including hot and cold rolling steps and a ynal heat treatment to; eil'ect age hardening, or precipitation` hardening, of the alloy steel, the arrangement and o sequence of 'the steps being suoli` that an article having a high surface inish suitable for direct plating vthereover without much if any polishing or bumng is produced.

Other and further important objects of this in- 10 vention will become apparent from the following description and appended claims.

On the drawing:

The gureillustrates schematically the various steps of the process-embodying my invention. l5 Suitable age hardenable alloy steels include steels containing relatively minor proportions of copper, or copper and aluminum, or vother known age hardening constituents. In the case oi' a copper alloy steel, the copper content may vary 2U between 0.5% and 3% but is preferably in the neighborhood of 1%. The carbon content may suitably be between 0.05 and 0.7%, with sulphur and phosphorus present in their customary minimum percentages.` Manganese and silicon 25 may be present within rather low limits of, say,

The balance is iron.

An ingot or billet of such age hardening steel, as prepared in a suitable steel making furnace, is first 'hot rolled into the desired Width of sec- 30 tions, but to a somewhat greater thickness of section than is desired in the final article. The temperature at'which the hot rolling is carried out may be betweenabout 1300 and 1900 F., although* temperatures at the start may be some- ,35 what higher than. this lupper limit, say 2200 F. After the hot rolling operation, the semi-iinished sheet is air cooled, or should-its composition so require, may be quenched in oil or water, so as to prevent yprecipitation of the age hardening con- 40 'stituenta In' other words, in the case of a copper alloy steel, the copper should be held in solution by whatever cooling step is employed. A certain amount of normalizing of the carbon content is also eected by the hot rolling and subsequent 45 air cooling steps.

The semi-tlnished sheet is next cleaned, as by vpickling, sand blasting or the like, and cold rolled to the desired thickness oi' the finished article.

The cold rolling is done between highly polished 5u rolls. so as to produce a high degree of surface on the rolled sheets. Thereafter, the sheets vare cut to lengthvand oiled to preserve the nish during the subsequent forming steps. A

Where the` iinished article is a bumper, the 5|;

semi-finished sheets are carried through two or more press operations", carried out with the steel cold and involving trimming and punching, forming to the desired shape and other usual steps.

The formed bumpers are then carried on a conveyor through successive washing operations to remove oil and lubricating compounds used in the pressing. 'Ihe cleaned bumpers are next subjected to a heat treatment in a furnace operated under controlled atmospheric conditions to age harden the steel without destroying the fine surface finish. Preferably, an atmosphere of a nonoxidizing or reducing character, but of a nondecarburizing nature, such as a mixture of hydrogen and carbon monoxide, or illuminating gas, is employed. The time of treatment in the furnace need be only sumciently long to eect a precipitation of the age hardening constituents, say from one to five hours, after which the bumpers are cooled, also in a non-oxidizing or reducing atmosphere, and delivered on the conveyor to a polishing machine or directly to the plating room, depending upon the perfection of the press work. Ordinarily, little if any bufling or polishing will be necessary in preparing the work for bright metal plating. i

Instead of performing the heat treatment in a furnace such as described, salt baths followed yby water quenching might be substituted. In either case, the temperature to which the bumper bars are subjected should be between about 350 and 650 C. in order to effect precipitation hardening of the alloy steel.

The foregoing method greatly decreases the cost of manufacture of bumper bars and like articles that are to be bright metal plated, since it largely eliminates the expensive polishing and bufing operations. If polishing is required, it is possible to start with a No. 150 polishing grain, instead of starting with a much coarser grain such as is now required in the usual operations employed in the manufacture of bumper bars. After a light polishing operation, if any is necessary, the bumper bars are ready for the plating operation. By employing a so-called bright nickel plating process, the bumper bars can be given a bright, mirror-like plating of nickel with a minimum of polishing or bumng necessary, and they may thereafter be directly chromium plated or not, as desired.

As an alternative procedure to that described above, the ingots or billets of age hardenable alloy steel may first be hot rolled to finished size, air cooled to normalize, polished as fiat pieces of steel, cold shaped into bumpers and the bumpers subjected to heat treatment to effect age hardening. The polishing step is thus substituted for the cold rolling step in the preferred process.

In the event that the early steps of the process have been so carried out that the age hardening constituents have been allowed to precipitate, prior to the nal heat treatment step, the bumpers may be heated to bring the age hardening constituents into solution, quenched with sufcient rapidity to maintain said constituents in solution and then reheated to cause their precipitation. l

I am aware that numerous details of the process may be varied through a wide range without departing from the principles of this invention, and I, therefore, do not purpose hunting the patent granted hereon otherwise than necessitated by the prior art.

I claim as my invention:

1. In the method of preparing steel bumper bars and like articles for subsequent nickel and chromium plating, the improvementin said method whereby polishing, of said articles in connection with said plating may be largely eliminated, said improvement comprising hot rolling an ingot of copper alloy steel, the copper content of said steel being between 0.5 and 3.0% and the carbon content being between 0.05 and 0.7%, air quenching the resulting semi-finished sheets to retain the copper content in solution in said alloy, pickling, cold rolling and forming said semi-nuished sheets into bumper bars, cleaning said bars and subjecting said bars in a non-oxidizing environment to heat treatment to effect precipitation of said copper content while maintaining the smooth surface characteristics of said bars produced by cold rolling. v

2. In the method of manufacturing steel bumper bars and like articles that are to be bright plated, the improvement in said method whereby polishing of said articles in connection with said plating may be largely eliminated, said improvement comprising yhot rolling an ingot of an age hardenable alloy steel at a temperature of between 1300 and 2200 F. to a semi-finished sheet of the desired width but of greater thickness than that of the finished article,.coo1ing said semifinished sheet to prevent precipitation of the age hardening constituents, pickling and cold rolling the sheet to the desired thickness and to a high surface `ilnish, trimming, punching and forming said sheet to the desired shape and subjecting the shaped article to heat treatment in a nonoxidizing environment to age harden the alloy steel while preserving the high surface flnish.

3. In the method of manufacturing steel bumper bars and like articles that are to be bright plated, the improvement in said method whereby polishing of said articles in connection with said plating may be largely eliminated, said improvement comprising hot rolling an ingot of an age hardenable alloy steel at a temperature of between 1300 and 1900" F. to a semi-finished sheet of the desired width but of greater thickness than that of the finished article, cooling said semifinished sheet to prevent precipitation of the age hardening constituents, pickling and cold rolling the sheet to the desired thickness and to a high surface finish, trimming, punching and forming said sheet to the desired shape and subjecting the shaped article to heat treatment in a non-oxidizing, non-decarburizing gaseous environment to age harden the alloy steel while preserving the high surface finish.

4. In the method of preparing bumper bars and like articles that are to be plated, the improvement whereby polishing of said articles prior to and after plating may be largely eliminated, said improvement comprising hot rolling an age hardenable steel of the copper alloy type into sheet form, cooling said sheet in such manner as to maintain the age hardening components of said alloy in solution, cleaning, cold rolling said sheet to reduce the thickness thereof and to impart thereto smooth surface characteristics and maintaining said smooth surface characteristics by subjecting said sheet in a non-oxidizing environment to heat treatment to effect precipitation of said age hardening components and thereby harden said steel.

' EDWIN M. BAKER. 

